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Potassium Channel Blocker (Neuromuscular Junction Facilitator)

Amifampridine

Brand names: Firdapse, Zenas

A potassium channel blocker used to treat the symptoms of Lambert-Eaton myasthenic syndrome in adults.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

It blocks presynaptic voltage-gated potassium channels, prolonging nerve terminal depolarisation and enhancing calcium-dependent acetylcholine release at the neuromuscular junction.

Prescribing in practice

  • It can lower the seizure threshold and is contraindicated in epilepsy, and it may prolong the QT interval so caution is needed with other QT-prolonging drugs.
  • It should be initiated and supervised by a specialist experienced in managing Lambert-Eaton myasthenic syndrome.
  • Because the syndrome is frequently paraneoplastic, an underlying malignancy (particularly small-cell lung cancer) should be excluded and monitored for.

Monitoring

Monitor clinically for seizures and consider electrocardiographic assessment where there are additional risk factors for QT prolongation.

Counselling the patient

  • Report any fits, twitching, or unusual heart sensations promptly.
  • Do not stop the medicine suddenly without specialist advice as symptoms may return.
  • Attend follow-up for ongoing screening related to the underlying condition.

Evidence & guidelines

Use is supported by its licensed indication for Lambert-Eaton myasthenic syndrome and specialist neuromuscular guidance.

Reference: NICE TA605 (Amifampridine for Lambert-Eaton myasthenic syndrome, 2020); Orphanet / European Neuromuscular Centre guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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